1. Field of the Invention
The invention generally concerns optical scanning systems, including systems having a high resolving power for scanning documents and the like to generate digital, binary data which represent the scanned information. The scanned information can then be stored electronically for later computer processing. There is a great need for a facility for the scanning of documents, drawings and similar materials, thereby saving storage space and facilitating corrections of drawings, etc.
2. Background of the Invention
Since scanning systems of this type are designed to scan very broad documents, the optical system in front of the actual scanning unit or the CCD camera will be utilized to the utmost. Thus, use is made of very expensive lens beams which are either mounted mechanically very stably or are stitched together, as shown in U.S. Pat. No. 5,117,295. The optical system is arranged stationarily in front of the CCD cameras, and the scanning unit is therefore borne with a constant resolution which depends upon the configuration of the documents, the lens system and the CCD cameras as well as the density of the photosensitive cells on the CCD camera.
If a variable resolution of the document of the scanned data is desired, such is provided by the subsequent data processing of the written data internally in the optical scanner. U.S. Pat. No. 4,631,598, U.S. Pat. No. 4,972,273 and U.S. Pat. No. 5,218,457 provide examples of such subsequent data processing. The analog signals from the CCD cameras are converted into digital signals, which takes place controlled by a periodic clock signal. If the resolution is to be enhanced, new grey level values are then estimated between already existing grey level values which are determined by sampling. According to the method disclosed in these documents it is not possible to select an arbitrary position of these estimated grey level values, because of the limitations imposed by the algorithms on which the method is based. Thus, it is not possible to choose an arbitrary resolution of the written data, which is generally desirable in many cases.
The object of the invention is therefore to provide an optical scanning system in which the resolution can be selected freely.
Another object of the invention is to provide an optical scanning system wherein the variable resolution enables compensation for imaging errors in the optical system of the scanner.